1. Field of the Invention
The present invention relates to a print head unit having an ink-jet print head, and relates more particularly to a mounting construction for a pressure damper that absorbs pressure variation in the ink inside the ink-jet print head.
2. Description of the Related Art
Ink-jet printers are widely and commonly used today as continuing improvements in ink-jet print head molding technology and ink discharge control technology have made it possible to freely control the placement of minute ink drops on recording media and achieve extremely high quality printing at high speed.
The surface condition of each ink nozzle is extremely important if stable printing results are to be achieved in an ink-jet printer; in other words it is necessary that ink forms an appropriate meniscus in each ink nozzle during printing. To achieve this, the pressure inside the path through which ink is supplied to the ink-jet print head, and, within the ink-jet head, to the ink nozzles must be kept constant. Ink stored in the ink tank travels through a flexible tube to the ink-jet print head. The ink-jet print head prints while the print head unit equipped with the ink-jet print head and a carriage is being moved according to a printing control command. As a result, the shape of the bend, that is, the curvature, of the tube whereby ink is supplied to the ink-jet print head changes as the print head unit moves. This destabilizes the ink pressure in the ink-jet print head, and creates the danger of the meniscus desirably formed in an ink nozzle being destroyed.
Some ink-jet printers are equipped with a pressure damper directly connected to the ink-jet print head to avoid this problem. The pressure damper typically has an ink reservoir that freely expands and contracts, and thus has a variable capacity. Ink supplied through the ink tube is temporarily stored in this ink reservoir, and the ink pressure inside the ink-jet print head is thereby held constant.
The substrate on which this ink-jet print head is mounted is normally fastened directly to the carriage in this type of printer. The pressure damper is fixed inside a particular case, and connection of the pressure damper to the ink-jet print head is assured by fastening the case to the carriage.
In other words, the ink outlet of the pressure damper is insertion fit to the ink supply inlet of the ink-jet print head when this case is fastened to the carriage, and a seal therebetween is thus held.
However, problems such as the following remain in a conventional ink-jet printer equipped with a pressure damper.
(1) Molding variations in the case, carriage, and pressure damper mean that even when the case is completely fastened to the carriage, the ink outlet of the pressure damper may not be completely connected to the ink supply inlet of the ink-jet print head. More specifically, dimensional tolerance caused by molding variations can create a gap or inclination between the bonding surfaces of the ink supply inlet and ink outlet, thus degrading the seal.
(2) External force acting on the case in which the pressure damper is housed is transferred directly to the pressure damper inside the case. This can adversely affect the connection between the ink supply inlet and ink outlet.
While the ink outlet of the pressure damper and the ink supply inlet of the ink-jet print head could be connected by an adhesive, for instance, to ensure a reliable connection, this would make it more difficult to replace or repair individual parts. It would become particularly difficult to install and remove individual pressure dampers to the ink-jet print head in a print head unit having plural ink-jet print heads each connected to a respective one of pressure dampers arranged next to one another.
Furthermore, a pressure damper must be provided for each of the colors used in color printers that use plural colors of ink. This increases the size of the print head unit. It is therefore desirable to make the print head unit as small as possible, particularly when plural pressure dampers are present.
Therefore, it is an object of the present invention to overcome the aforementioned problems by providing a print head unit that reliably connects the ink outlet of the pressure damper to the ink supply inlet of the ink-jet print head.
It is a further object of the invention to minimize the effect on the pressure damper of external force applied to the case housing the pressure damper, and thus prevent any such external force from affecting the connection between the ink supply inlet and ink outlet.
Yet a further object of the invention is to reduce the size of the print head unit.
To achieve these objects, a print head unit, according to one aspect of the present invention, is provided. The print head unit comprises an ink-jet print head having an ink supply inlet, a first support member (preferably a carriage) in which the ink-jet print head is formed, a pressure damper for absorbing pressure variation in the ink in the ink-jet print head, and a second support member (preferably a case) that is removably connectable to the first support member and supports (houses) the pressure damper. The pressure damper has an ink outlet that is removably connectable to the ink supply inlet, and the second support member supports the pressure damper movably in the connect/disconnect direction of the ink outlet to the ink supply inlet. In addition, the print head unit further includes a biasing element for pushing the ink outlet of the pressure damper to the ink supply inlet.
Thus comprised, the ink outlet can be reliably connected to the ink supply inlet, even if there are molding variations in the cases and/or pressure damper because the biasing element pushes the pressure damper to the ink-jet print head.
The pressure damper further preferably has a seat at a back part of the ink outlet, and the biasing element pushes against the seat.
Yet further preferably, the biasing element is a spring extending between the seat and an inner wall of the second support member.
Yet further preferably, the second support member has a guide for limiting movement of the pressure damper in a direction other than the connect/disconnect direction.
Yet further preferably, an opening for exposing the ink outlet of the pressure damper is provided in the bottom wall of the second support member, and an opening for exposing part of the top of the pressure damper is provided in the top wall of the second support member.
Yet further preferably, the pressure damper further comprises a pin protruding externally from the opening provided in the top wall of the second support member. Thus, when the force of the biasing element alone is not enough to connect the pressure damper and ink-jet print head, this pin can be depressed to push ink outlet to ink supply inlet, and thereby positively press fit ink supply inlet into ink outlet.
Yet further preferably, the first support member holds a plurality of ink-jet print heads, and the second support member supports a plurality of pressure dampers, one corresponding to each of the ink-jet print heads. In this case the pressure damper preferably has a circumferential surface between two parallel sides, and the ink supply inlet, ink outlet, and pin are formed on the circumferential surface. The size of a print head unit having a plurality of ink-jet print heads can thus be reduced.
The above-described print head unit may be part of a printing mechanism embodied in a printer, such as an ink-jet printer.
In another aspect, the invention may be embodied in a method of making a print head unit, such as the one described above.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.